1. Field of the Invention
The present invention relates to a speech recognition method and a speech recognition apparatus for recognizing an uttered word and a speech control system for controlling an electric apparatus according to the recognized word.
2. Description of the Related Art
2.1. Previously Proposed Art
In a conventional speech recognition method, voice samples of a plurality of words desired to be recognized are registered as registered words in advance in a recognition word dictionary, and a word uttered by a user is recognized by using the recognition word dictionary. In this case, because it is difficult that a user knows all words registered in the recognition word dictionary, the user cannot avoid to utter a word other than the registered words. Therefore, even though the user utters a word other than the registered words, a specific word, of which an acoustic distance from the uttered word is shortest among those of the registered words, is selected from the registered words as a recognized word. As a result, in cases where the conventional speech recognition method is used for a conventional speech control system, there is a problem that an uttered word other than the registered words is erroneously recognized and an electric apparatus controlled by the speech control system is erroneously operated.
To prevent this problem, a word recognition score indicating a degree of an acoustic distance between the uttered word and a recognized word is calculated when the recognized word is determined, and the recognized word is adopted in cases where the word recognition score is higher than a threshold value. In contrast, in cases where the word recognition score is equal to or lower than the threshold value, the recognized word is rejected. That is, the recognized word is not adopted.
Therefore, an uttered word other than the registered words is not erroneously recognized because the word recognition score for the uttered word other than the registered words is low.
2.2. Problems to be Solved by the Invention
However, in cases where the word recognition score is calculated, it is required to adjust the threshold value according to environmental conditions (for example, noise conditions) of both the user and the speech control system. Also, it is required to set the threshold value changeable according to the combination of the registered words. Accordingly, there is a problem that it is difficult that the threshold value is set so as to reliably reject an uttered word differing from any registered words and to accurately recognize an uttered word agreeing with one of the registered words.